<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Reference</title>
<style>
.clamp {
  font-size: 16px / 16px serif;
  white-space: pre-wrap;
  background-color: yellow;
}
ruby.under {
  ruby-position: under;
}
</style>
<div class="clamp">Line 1
Line 2
<ruby class="under">Line 3<rt>ruby</ruby>…</div>
